There is disclosed herein, layered imaging members such as multi-layered photoreceptors utilized in electrophotography. The layered imaging members include an undercoat composition that produces enhanced hole or electron blocking layer properties. The embodiment finds particular application in conjunction with systems for printing and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
An electrophotographic imaging member device comprising at least one photoconductive insulating layer is imaged by uniformly depositing an electrostatic charge on the imaging surface of the electrophotographic imaging member and then exposing the imaging member to a pattern of activating electromagnetic radiation, such as, light which selectively dissipates the charge in the illuminated areas of the imaging member while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking toner particles on the imaging member surface. The resulting visible toner image can then be transferred to a suitable receiving member such as paper.
A number of current electrophotographic imaging members are, for example multilayered photoreceptors that, in a negative charging system, comprise a substrate support, an optional electrically conductive layer, an optional charge or hole blocking layer, an optional adhesive layer, a charge generating layer, a charge transport layer, and optional protective or overcoating layer(s). The imaging members of multilayered photoreceptors can take several forms, for example, flexible belts, rigid drums, flexible scrolls, etc. Flexible photoreceptor belts may either be seamed or seamless belts. In a typical flexible photoreceptor belt design, an anti-curl layer may, for example, also be employed on the backside of the flexible substrate support, the side opposite to the electrically active layers, to achieve the desired photoreceptor belt flatness.
After formation of an electrically conductive surface, a charge blocking layer, hereinafter referred to as a hole blocking layer, may be applied thereto for photoreceptors. Generally, hole blocking layers for positively charged photoreceptors allow holes from the imaging surface of the photoreceptor to migrate toward the conductive layer and hole blocking layers for negatively charged photoreceptors allow electrons from the imaging surface of the photoreceptor to migrate toward the conductive layer. As a result, the hole blocking layer is an electronic barrier to holes or electrons between the adjacent photoconductive layer(s) and the underlying conductive layer. The compositions which comprise the hole blocking layer may be applied by any suitable conventional techniques to produce a dry thickness of less than about 0.2 micrometer.
Many currently available charge or hole blocking layers consist of particulates of metal oxides dispersed in polymeric binders. For example, one such composition utilizes titanium dioxide and silica dispersed in a phenolic resin. However, many of such compositions suffer from short cycle life with early CDS (charge deficient spots) printouts during cycling and/or exhibit a number of large spot printout defects.
In this regard, stable cycling is preferred for photoreceptors. Any cycling up or cycling down is undesirable. Additionally, printout defects are also undesirable. These defects are caused by the penetration of carbon fiber(s) through the multilayer array of the photoreceptor to the substrate. This produces a conductive path across the photoreceptor, thus resulting in black spot defects.
Additionally, silica is utilized in conventional compositions to suppress “plywooding”. Plywooding refers to the formation of unwanted patterns in electrostatic latent images caused by multiple reflections during light exposure of a charged imaging member. When developed, these patterns resemble plywood. Silica is a micro particle that may be added to the composite to scatter light, thus minimizing the plywood-like print patters. However, the use of silica in conventional compositions is believed to contribute to early charge deficient spots during cycling.
Hence, it would be desirable to provide an undercoat composition for producing charge or hole blocking layers with longer cycle life stability. Additionally, it would be beneficial to provide an undercoat layer which inhibits carbon fiber penetration to the substrate and which minimizes large spot printing defects.
The present exemplary embodiment contemplates new and improved undercoat compositions for forming hole blocking layers, and the longer life, imaging members produced therewith, which overcome the above-referenced problems and others.